1. Field of the Invention
The present invention relates to a zoom lens mechanism, as used in a camera, and its assembling method, and particularly relates to the zoom lens mechanism in which a linear actuator is used, and its assembling method.
2. Description of the Related Arts
Conventionally, a general zoom lens mechanism has a construction in which a plurality of cylindrical members, like cam cylinders, are arranged one above the other on an outer circumference of a lens group.
Meanwhile, conventionally, a so-called suspended type of lens barrel has a construction in which there are installed a guide bar for linearly guiding a holder that holds a lens group, a cam plate for moving the holder, and the like, around the lens group.
In this way, according to the conventional zoom lens mechanism, there are mounted various components and parts around the lens group. Consequently, the zoom lens mechanism increases in its radial size around the entire periphery of the lens group.
On the other hand, in recent years, there is an increasing demand for making more compact and smaller an image-taking element in fields of a video camera, a digital camera, and the like, and at the same time for making smaller the zoom lens mechanism itself, in order to realize a thinner type of a video camera, a digital camera, and the like.
However, according to the conventional zoom lens mechanism, the radial size around the whole periphery of the lens group is large. Accordingly, it is difficult to make thinner and smaller the zoom lens mechanism itself.
On the other hand, according to a conventional zoom lens mechanism, a plurality of lens groups with different zooming components are held by lens holders, respectively, in which each lens holder is supported by a lens support mechanism and is moved along an optical axis by an interlocking device. That is, the plurality of lens groups are moved for zooming operation by the movement of the lens holders which are driven by the lens support mechanism.
Such a conventional zoom lens mechanism is assembled usually with the following steps.
First, the lens groups are built in lens holders, respectively. In this process, one lens or more than one lens in the lens group is positioned with respect to the lens holder.
Next, the lens support mechanism is assembled together with the lens holder which the lens group is built and set in. That is, the lens holder is assembled at the same time while the lens support mechanism is assembled. This means that a lens holder is not built in a lens support mechanism the assemblage of which is already finished. In the zoom lens mechanism that has once been assembled in this way so that the lens support mechanism supports the lens groups, its precision or accuracy in alignment or positioning of each lens group with respect to the optical axis is affected by the component precision of each lens holder, the precision or accuracy in positioning of each lens with respect to the lens holder, and the precision or accuracy in assemblage of each lens holder relative to the lens support mechanism.
Next, the position of the lens group is adjusted from the front end and/or rear end of the zoom lens mechanism. More specifically, in case that the zoom lens mechanism is once assembled, the lens group placed at the front end and/or rear end thereof is aligned relative to the optical axis. With the adjustment of the lens group relative thereto, it is possible to attain a desired precision thereof.
In order to adjust the alignment of the lens group placed at the front end and/or rear end relative to the optical axis, it is generally necessary to perform such a troublesome work as pushing an outer circumferential surface of the lens mounted in the lens frame in the axial direction, with a force of access thereto in the same axial direction so as to slide and displace the lens in small steps bit by bit in its radial direction.
However, as to the lens groups being positioned at intermediate positions other than such lens groups being positioned at the front and rear ends thereof, it is not possible to adjust the alignment of those lens groups relative to the optical axis, because of a difficulty in getting an access thereto due to an interference by the arrangement in which there are mounted some parts to constitute the lens support mechanism around them.
As already explained, in recent years, there is an increasing demand for making more compact and smaller an image-taking element in fields of a video camera, a digital camera, and the like, and at the same time for making smaller the zoom lens mechanism itself, in order to realize a thinner type of a video camera, a digital camera, and the like. In case that the zoom lens mechanism is miniaturized, the allowance in error of decentering the lens group with respect to the optical axis also becomes smaller. This makes it necessary to align the lens group relative thereto with much higher precision than the precision of the conventional zoom lens mechanism.
However, because the work to adjust the lens groups at the front and rear ends thereof relative to the optical axis, is so troublesome even in the conventional zoom lens mechanism, it is quite more difficult to align them relative thereto with much higher precision by the same method as the conventional one.
Further, it is difficult to attain a desired high precision without aligning the lens groups at intermediate positions relative to the optical axis, as in the conventional mechanism.
On the other hand, conventionally, there has been provided a linear actuator, as used as a driving unit of the zoom lens mechanism, which is specially used for a precision equipment such as a video camera.
For example, U.S. Pat. No. 5,225,941 discloses a linear actuator 500, as shown in FIG. 15. According to the construction, a bar-shaped engaging member 508 is fixed to one end face 504 of a lamination type of piezoelectric device or an electromechanical transducer 502. The device 502 includes a lamination of a plurality of piezoelectric elements that generate a displacement of expansion and contraction, responsive to a predetermined electrical signal supplied to the electromechanical transducer 502. The one end face 504 of the piezoelectric device 502 is in the direction of the displacement of expansion and contraction, i.e. in the direction of the lamination of the plurality of piezoelectric elements of the electromechanical transducer 502.
The other end face 506 of the electromechanical transducer 502 in the direction of the displacement is fixed to a fixing member 509. A member to be driven 510 is slidably supported by the engaging member 508 and a guide bar 514 which is fixed in parallel to the engaging member 508. That is, the engaging member 508 is inserted into a sliding contact hole 512 of the member to be driven 510, and the sliding contact hole 512 of the member to be driven 510 is pressed against the engaging member 508 by a springly repulsive force of a plate spring 516 which is screwed to the member to be driven 510. With the construction, the engaging member 508 and the member to be driven 510 are frictionally engaged with each other.
The individual piezoelectric elements of the electromechanical transducer 502 expand when a predetermined voltage is applied thereto. Therefore, the linear actuator 500 enables the member to be driven 510 to move along the bar-shaped engaging member 508 due to the expansion and contraction of the electromechanical transducer 502 in the direction of displacement thereof, when a periodical voltage is applied to the electromechanical transducer 502.
More specifically, for example, the member to be driven 510 can be driven intermittently or periodically in small steps bit by bit along the bar-shaped engaging member 508 by applying a voltage to the electromechanical transducer 502 in such a manner that its expanding speed and contracting speed of the electromechanical transducer 502 are different from each other, and that there alternately occurs a slide between the member to be driven 510 and the bar-shaped engaging member 508, and a feed of the member to be driven 510 and the bar-shaped engaging member 508 relative to the fixing member 509.
Explaining more in detail in terms of the principle of how the linear actuator operates, when the engaging member 508 moves slowly relative to the fixing member 509, the member to be driven 510 moves along with the engaging member 508 by a frictional force exerting between the member to be driven 510 and the engaging member 508. That is, there is no slide between the member to be driven 510 and the engaging member 508.
Meanwhile, when the engaging member 508 moves faster or quicker than a certain level in speed, and when an inertial force of the member to be driven 510 surpasses the frictional force exerting therebetween, there occurs a slide at a frictional engaging portion between the member to be driven 510 and the engaging member 508, so that the member to be driven 510 remains stationary or almost stationary relative to the fixing member 509 while only the engaging member 508 moves relative thereto.
Namely, the member to be driven 510 is fed together with the engaging member 508 at time of driving the engaging member 508 in one direction, and the member to be driven 510 is slid relative to the engaging member 508 so as to be stationary or almost stationary relative to the fixing member 509 at time of driving the engaging member 508 in the other direction. And, the operation is repeated intermittently or periodically, to make it possible to move the member to be driven 510 in the one direction intermittently or periodically relative to the fixing member.
However, according to the linear actuator 500, a long engaging member 508, fixed to the one end face 504 of the electromechanical transducer 502, is used. Therefore, a large space for the engaging member 508 must be set aside in the linear actuator, resulting in difficulty in realizing a compact actuator.
Furthermore, according to the conventional linear actuator 500, its vibrating system including the bar-shaped engaging member 508 is longer; therefore, its resonance point, etc. is lower. Namely, the frequency able to be used in driving the linear actuator 500 is limited to a lower range thereof, thus making it difficult to improve its driving capacity and performance.